In a fresh blow to the scandal-ridden Royal family, The Sun reported that Princess Diana was given the order by senior Royals after she confessed on TV to having an affair with Major Hewitt.
The DNA test confirmed that Prince Charles is Harry's father.
Princess Diana's love interest not to marry
In her new book 'Diana: The Last Word', the Princess' long-time friend Simone Simmons said she was shown a letter demanding the blood test.
49-year-old Simone said Diana was upset over the whispers about parentage of his younger son, who had red hair like Hewitt, and for making his son undergo the test. But she said "At least having the test put paid to all the rumours."
According to the report, Prince Philip hit the roof when he heard rumours that Hewitt was "the father" of Prince Harry. But the young Prince, aged 11 at the time, was never told the reason for the test. His brother William was also tested, with the same result.
Diana was pregnant when she died: Report
"Energy healer" Simone said Diana showed her a typed letter demanding the tests. It arrived following her Panorama admission about former Army officer Hewitt to Martin Bashir in November 1995. She would not confirm that Prince Philip was the author of the letter.
Simone, who shared hours of heart-to-heart conversations with Diana and was entrusted with her letters, recalled that whispers about Prince Harry's parentage were circulating nationwide at that time.
They had even reached Buckingham Palace.
Diana on her lover, marriage and royal life
She said in her book "It fell to me to impart that unpleasant news to the Princess. She was forever asking me what people were saying about her. One day I took a deep breath and told her that the rumour doing the rounds was that Hewitt was the father of Prince Harry.
She took it very seriously. She said: "If people worked the dates out properly they would see that it's nothing to do with Hewitt.
"It's pretty obvious he's a Windsor. In colouring he's a Spencer, but he has Charles' eyes."
Diana was told in no uncertain terms that her sons should have a blood test and, of course, everything was as it should have been.
And Hewitt himself has always denied paternity. The gossip had reached Prince Philip and further undermined an "already tense relationship between Diana and her father-in-law."
Simone said Diana also had a nasty letter from Princess Margaret, accusing her of letting the Royal Family down.
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